52 



EDWIN W. HUMPHREYS AND ALEXIS A. J V LIEN 



Fig. 5. — Fracture and faulting shown by one of the 

 transported slabs. 



under the bowlder, the folia of the granite showed differentiation 



and deformation as by a crushing force from above; but the lower 



level of the slab 

 rarely showed much 

 if any depression in 

 a direction below the 

 bowlder (Figs. 7 and 

 8). 



Cause of decay. — ■ 

 In seeking to account 

 for this peculiar de- 

 composition in one 

 tract of the schist, 

 the action of the 

 weather is barred 

 out, on account of 

 the absence of such 



decomposition in adjoining areas of schist, as well as in the other 



pegmatite dikes of the Bronx region, the absence of concentration 



of iron oxide from 



agencies of mere 



oxidation, 1 and the 



sharp line of de- 



markation between 



this tract and the 



unchanged schist. 



All the facts point to 



some agency which 



could produce deep 



local corrosion, and 



the considerable 



leaching shown by 



the removal of iron 



oxide and by the 



residues of white kaolin. The presence of the pegmatite dike 



across the middle of this tract, and its parallelism to the sharply 



1 Stremme, Zts.f. prkt. Geo!., XVI (1908), 128. 



Fig. 6. — Curvature produced by pressure on a trans- 

 ported slab. 



